The prior art gives the person skilled in the art many examples of magnetometric devices, in particular by the patent documents U.S. Pat. No. 4,893,076 and U.S. Pat. No. 4,611,127.
When measuring a magnetic field, either so as to ascertain the value thereof or so as to ascertain the value of another physical parameter which changes as a function of the measured magnetic field, and when the magnetic field to be measured is not the terrestrial magnetic field, the measurement obtained must be corrected of the value of the terrestrial magnetic field.